When one of the long bones of the body, such as the femur, is fractured, treatment of the fractured bone requires that the parts of the bone at the fracture site be substantially immobilized in abutting relationship during the knitting process. Any longitudinal, transverse, or rotational movement of one section of bone relative to the other delays the healing process, and can completely undo the progress of the reuniting of the bone sections. In general, two different approaches have been used to accomplish the desired ends of immobilization and longitudinal compression sufficient to maintain the bone sections in contact.
One approach involves driving metallic pins through the two sections of bone to be joined, and connecting them to one or more plate members bearing against the bone sections externally thereof, as shown in U.S. Pat. No. 4,776,330 of Chapman et al. Such an arrangement injures the flesh and muscle surrounding the bone, and the multiplicity of pins driven through the bone tend to weaken its hard outer layer. Plates also tend to stress-shield the bone and it does not become strong underneath the plates, and plates are not always able to bear sufficient stress for many applications. Equally as important is the necessity of subjecting the patient to two major operations, one to install the plates and pins, and one to remove them after healing. Any invasion of the body gives rise to the possibility of infection, therefore such invasions should be minimized if at all possible.
A second approach to treating problems of the femur, for example, involves the use of an intramedullary nail which is inserted into the bone channel and affixed therein by any of a number of ways. Intramedullary fixation is advantageous because it allows the femur, for example, to bear full weight and undergo normal stimulation for growth and renewal. One such arrangement is shown in U.S. Pat. No. 3,717,146 of Halloran. wherein a threaded, slotted nail is driven into the medullary canal of the femur, with the threads on the exterior of the nail engaging the interior walls of both sections of bone to align them and pull them together in compression. After healing of the bone at the break the nail may be removed through a hole drilled in the upper or proximal end of the femur. For additional strengthening, a compression plate may be used at the fracture site.
U.S. Pat. No. 4,091,807 of Aginsky discloses a split nail which is inserted in the medullary canal and one end portion of the nail is expanded by a screw actuated expansion wedge to grip the inner wall of one section of the fractured femur. The other end of the nail is anchored to the proximal end of the femur, and continued rotation of the wedge actuating screw pulls the two sections of the femur together in compression and in alignment. The nail is removed after the bone is healed. Another example of a removable intramedullary nail is shown in U.S. Pat. No. 4,805,607 of Engelhardt et al.
Some arrangements dispense with the intramedullary nail approach and utilize instead members inserted into each bone section and anchored thereto, and a central alignment pin which is slidable, but not rotatable, in the members in each bone section. These arrangements are all designed to remain permanently within the medullary channel. Typical of such arrangements are those shown in U.S. Pat. Nos. 4,467,794 of Maffei, 4,016,874 of Maffei et al and 4,262,665 of Roalstad.
Among the advantages of the nail arrangement are the necessity, usually, for only one incision in the patient's buttock, for example, while the fracture is being reduced and the nail passed through the bone sections, and the relatively easy removal of the nail after the healing process is completed. On the other hand, the nails as such do not prevent rotation of the bone sections relative to each other, which can be as damaging as sudden tension applied to the break area. One remedy for this problem is the use of a cross nail as shown in U.S. Pat. No. 4,697,585 of Williams. The cross nail is mounted in a slot cut in the neck and head of the proximal end of the femur and has a bore through which the intramedullary nail passes. A suitable set screw arrangement firmly joins the cross nail to the intramedullary nail so that there can be no rotation therebetween, and the distal end of the intramedullary nail is fixed in position by pins extending through the bone and the nail. With such an arrangement, rotation of the bone sections relative to each other is prevented. A variation of the cross nail arrangement is shown in the aforementioned Chapman et al patent.
In all of the foregoing arrangements, trauma centers must keep an inventory of incremental nail lengths so that a random, diverse incoming patient population may be accommodated. In those cases where permanent bone inserts are to be used, a premium is placed upon a close estimate of the patients correct bone length since, once installed, the apparatus is not adjustable, nor is it easily replaced. Intramedullary nails of differing lengths can be substituted for those in place, however, at least at the early stages of the bone healing, the fracture must be reduced again, necessitating a second operation on the patient.
In some cases, as in congenital abnormalities, it is desirable to lengthen the femur of the patient, or to correct leg length discrepancies. Leg or femur lengthening procedures include an external "halo" brace surrounding the leg, with crossed pins driven through the flesh and the bone on either side of a bone separation, and external screws extending between proximal and distal braces. Such an arrangement is both cumbersome and difficult to install, and limits the patient's movements and can cause continuing damage to flesh and muscle. Because the pins remain penetrating the flesh and skin, infection is a constant danger. Another common method for relatively short lengthening of the femur, for example, is bone grafting, which is a painful process and requires invasion surgery for each graft.
In none of the foregoing prior art arrangements is provision made for adjusting the lengths of the intramedullary device after insertion, thus the proper length of the bone after reduction of the fracture can only be estimated, and an intramedullary device of an estimated proper length inserted. In addition, bone lengthening can only be accomplished with an externally adjustable device, or by means of a grafting operation, or by completely replacing the nail.